EFFECTS OF ATP-SENSITIVE K-CHANNEL ACTIVATORS ON TRANSMITTER RELEASE PARAMETERS AT THE FROG NEUROMUSCULAR-JUNCTION()

The frog neuromuscular junction was used to study K(ATP) channel actio n and its relation to transmitter release. Diazoxide (10 muM) and crom akalim (300 muM) decreased the amplitude of the end-plate potential (E PP) without significantly affecting the miniature end plate potential (MEPP) amplitude. Thus, there was a significant decrease in the quanta l content of EPP after administration of the K(ATP) channel activators . These agents did not alter MEPP frequency or resting membrane potent ial (RMP). The diazoxide-induced decrease in EPP amplitude was antagon ized by the K(ATP) blocker glibenclamide (10 muM) suggesting K(ATP) ch annel involvement. Glibenclamide (10 muM) by itself caused a significa nt decrease in the RMP without significantly affecting the parameters of transmitter release. The diazoxide-induced decrease in EPP amplitud e was not readily reversible with washing, however, when glibenclamide was added after diazoxide, the effect was easier to reverse. The resu lts indicate that the activators exert their effect predominantly at t he presynaptic region.